What is 'z' if the confidence interval is 80%?

1 Answer
Jan 28, 2017

z=1.28; z=-1.28

Explanation:

Probability is 80% or 0.8

0.8 is evenly distributed on either side of z = 0

Find the nearest probability value or area in the table. It is 0.3997.
z value corresponding to 0.3997 is 1.28.

On the positive side we have 1.28 and negative side we have - 1.28

enter image source here